Shock absorber

ABSTRACT

In the shock absorber wherein the operation of the main valve for opening and closing a main oil channel by the action of the energizing current flowing through a linear solenoid thereby to control the damping power, an improvement in the response property of the main valve responsive to the change in moving amout of the piston or change in the set thrusting power of the linear solenoid. 
     The shock absorber comprises a main chamber facing to one end of the main valve so as to transmit the hydraulic pressure in the high pressure side main oil chamber for biasing said main valve toward the direction for opening said main oil channel, a pilot chamber facing to the other end of said main valve, a pilot valve for receiving the pressure in the main chamber to be opened to release the pressure in said pilot chamber to the low pressure side main oil chamber, a linear solenoid for biasing the pilot valve to the closing direction, a variable orifice having a variable opening area varied by the relative movement of said pilot and main valves, a pilot flow channel extending from said main chamber through the variable orifice and through the pilot valve to the low pressure side main oil chamber.

BACKGROUND OF THE INVENTION

The present invention relates to a shock absorber by which the dampingpower thereof is controlled by the electric current for energizing thelinear solenoid.

In the shock absorber used on vehicles, such as automobiles, motorbicycles or like, it is desirous that the damping power thereof isfreely varied depending on the cruising conditions. For example, asystem has been made known to the public, wherein the amount and rate ofexpansion or compression are detected so that the pressure for actuatinga main valve, which is provided in the piston for opening and closingthe oil passage, is freely varied by controlling energization of thelinear solenoid continuously or discontinuously during each stroke ofthe piston (for example, by Unexamined Japanese Patent Publication No.261528/1989 (corresponding to U.S. Pat. No. 5,090,525 and EuropeanPatent Publication No. 0330634A)).

The shock absorber used therein has the construction as shown in theschematic principle in FIG. 1. The shock absorber comprises a piston 16for defining two main oil chambers 12, 14 in a cylinder 10, a main valve22 provided in the piston 16 for defining a main chamber 18 and a pilotchamber 20, and an orifice 24 interposed between these main and pilotchambers 18, 20. The hydraulic pressure in the high pressure side mainoil chamber 12 or 14 is transmitted to the main chamber 18. On the otherhand, as the internal pressure in the pilot chamber 20 exceeds thethrusting power set by a linear solenoid 26, said main valve 22 is movedto open a main oil channel 28 (28a, 28b), which communicates with thetwo main oil chambers 12, 14, so as to control the damping power.Meanwhile, the in interior side of the main oil channel 28a is definedto be annular to surround the outer periphery of the main valve 22.

In this precedingly proposed system, the pressure in the high pressureside main oil chamber 12 or 14 is transmitted through the main chamber18 and the orifice 24 to the pilot chamber 20. And, when the pressure inthis pilot chamber 20 (Pilot Chamber Pressure P_(p)) exceeds the setthrusting power P_(s) of the linear solenoid 26 a pilot valve 30 isopened. Then, under the action of pressure drop upon passage of fluidmedium through the such orifice 24 and opening of the pilot valve 30,the pilot chamber pressure P_(p) at the downstream of the orifice 24becomes lower than the pressure in the main chamber 18 (Main ChamberPressure P_(m)). Thus caused pressure difference (P_(m) -P_(p)) urgesthe main valve 22 to move upwards. Reference numeral 31 designates aspring to restore the main valve 22.

Since the pilot valve 30 is opened the pilot chamber pressure P_(p), asdescribed above, the increment of the pilot chamber pressure P_(p) isdelayed owing to the interposition of the orifice 24. Such delayedresponse arises a problem that the response of the main valve 22 to thechange in set thrusting power P_(s) of the linear solenoid 26 isdelayed.

In order to provide a quicker response in dumping the pressure in thepilot chamber, the inventor has proposed to provide the pilot valve witha valve shaft extension that passes through the main valve and isexposed to the pressure in the main chamber. This arrangement permits amore rapid opening of the pilot valve when the pressure exceeds theforce of the linear solenoid. In order to improve this operation, it isnecessary to provide a restrictive orifice in the conduit connecting themain chamber to the pilot chamber. Because of this orifice, there is adelay in the return motion of the main piston.

Another feature of the invention has been accomplished in view of thecircumstances as aforementioned, and the object thereof is to provide ashock absorber by which the response property of the main valveresponsive to change in movement of the piston or change in setthrusting power of the linear solenoid is improved.

As has been noted, a linear solenoid is employed with the constructionsfor holding the pilot valve in its closed position. The force necessaryto cause opening of the control valve varies by varying the powerapplied to the solenoid and in this way the operation of the shockabsorber can be very effectively controlled. However, if there is amalfunction in the electrical operation, then the operation of the shockabsorber becomes uncontrolled.

It is, therefore, a still further object of the invention to provide animproved shock absorber of this type wherein the shock absorbingfunction can revert to a manual control in the event of an electricalfailure.

SUMMARY OF THE INVENTION

According to a first feature of the invention, the aforementioned objectis attained by the provision of a shock absorber characterised bycomprising a piston for defining two main oil chambers in a cylinder, amain oil channel for communicating said two main oil chambers, a mainvalve for opening and closing the main oil channel, a main chamberfacing to one end of the main valve so as to transmit the hydraulicpressure in the high pressure side main oil chamber for biasing saidmain valve toward the direction for opening said main oil channel, apilot chamber facing to the other end of said main valve, a pilot valvefor receiving the pressure in the main chamber to be opened to releasethe pressure in said pilot chamber to the low pressure side main oilchamber, a linear solenoid for biasing the pilot valve toward theclosing direction, a variable orifice having a variable opening areavaried by the relative movement of said pilot and main valves, and apilot flow channel extending from said main chamber through the variableorifice and through the pilot valve to the low pressure side main oilchamber.

Meantime, a valve shaft extending through the main valve to have one endfacing to the main chamber and biased by the linear solenoid may beprovided so that a variable orifice is formed by a passage providedthrough the valve shaft and the main valve. A fixed orifice may beprovided additionally in this passage.

The main chamber, to which the one end of the main valve is faced, maybe an isolated chamber to which the pressure in the high pressure sidemain oil chamber is transmitted through a one-way valve. However, themain valve may have one end provided with an annular stepped portion andan end face directly facing to one of the main oil chambers while thepressure in the other main oil chamber is transmitted to the steppedportion. In such a case, it is desirous that the pressure-bearing areasof the stepped portion and the end face should be differentiated fromeach other. Alternatively, a main pressure chamber may be formed in acylindrical body which extends through the main valve, so that avariable orifice is provided by a pin, which extends from the such mainpressure chamber through the pilot chamber to abut against the valvebody, and the cylindrical body.

Another feature of the invention is also adapted to be embodied in ashock absorber that is comprised of a pair of relatively movablecomponents defining a first fluid chamber. A second fluid chamber isalso provided and a first conduit interconnects the fluid chambers forflow therebetween and includes a control valve for controlling the flowthrough the first conduit. The control valve has a first surface exposedto pressure in the first fluid chamber and a second surface opposed tothe first surface and exposed to the pressure in a pilot chamber. Apilot valve selectively communicates the pilot chamber with a lowerpressure area. A linear electrical solenoid applies a predeterminedclosing force on the pilot valve. A second conduit containing a variableorifice interconnects the first fluid chamber to the pilot chamber fortransmitting pressure thereto. The effective area of the variableorifice is controlled by the position of at least one of the valves.

Another feature of the invention is adapted to be embodied in a shockabsorber comprised of a pair of relatively movable components defining afirst fluid chamber. A second fluid chamber is interconnected to thefirst fluid chamber by a first conduit which includes a control valvefor controlling the flow through the first conduit. The control valvehas a first surface exposed to the pressure in the first fluid chamberand a second surface opposed to the first surface and exposed to thepressure in a pilot chamber. A pilot valve selectively communicates thepilot chamber with a lower pressure area. A linear electrical solenoidapplies a predetermined closing force upon the pilot valve. A secondconduit interconnects the first fluid chamber to the pilot chamber fortransmitting pressure therebetween and an orifice is provided in thissecond conduit. A portion of the pilot valve extends through the controlvalve and is exposed to the pressure in the first fluid chamber forurging the pilot valve toward an open position in opposition to theforce of the linear electrical solenoid.

A yet further feature of the invention is also adapted to be embodied ina shock absorber comprised of a pair of relatively movable componentsdefining a first fluid chamber. A second fluid chamber is interconnectedwith the first fluid chamber for flow therebetween by a first conduit inwhich a control valve is provided for controlling the flow through thefirst conduit. The control valve has a first surface exposed to thepressure in the first fluid chamber and a second surface opposed to thefirst surface and exposed to the pressure in a pilot chamber. A pilotvalve is provided for selectively communicating the pilot chamber with alower pressure area. A linear electrical solenoid applies apredetermined closing force upon the pilot valve. A second conduitinterconnects the first fluid chamber to the pilot chamber fortransmitting pressure therebetween. A biasing spring is provided in forurging the pilot valve to a closed position for maintaining apredetermined opening force for the pilot valve in the event the linearelectric solenoid becomes inoperative.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing a shock absorber partially inschematic form and constructed in accordance with the prior art.

FIG. 2 is a partially schematic cross-sectional view, in part similar toFIG. 1, and shows a first embodiment of the invention.

FIG. 3 is a partially schematic cross-sectional view, in part similar toFIGS. 1 and 2, and shows a second embodiment of the invention.

FIG. 4 is a partially schematic cross-sectional view, in part similar toFIGS. 1-3 and shows a third embodiment of the invention.

FIG. 5 is a partially schematic cross-sectional view, in part similar toFIGS. 1-4 and shows a fourth embodiment of the invention.

FIG. 6 is a cross-sectional view of a shock absorber constructed inaccordance with a fifth embodiment of the invention.

FIG. 7 is a partially schematic cross-sectional view of a shock absorberconstructed in accordance with a sixth embodiment of the invention.

FIG. 8 is a partially schematic cross-sectional view of a shock absorberconstructed in accordance with a sixth embodiment of the invention.

SUMMARY OF THE INVENTION

A first embodiment of the invention is shown in FIG. 2 and includes manyof the components of the prior art type of construction. Where that isthe case, those components have been identified by the same referencenumerals as applied in FIG. 1 and will not be described again, exceptinsofar as is necessary to understand the construction and operation ofthis embodiment. This embodiment is intended to improve upon theconstruction of the prior art by increasing the responsiveness of theopening of the pilot valve.

As shown, a valve shaft 32 is provided integrally with the plunger ofthe solenoid 26 on the pilot valve 30 so that the valve shaft 32 extendsthrough the pilot chamber 20 and the main valve 22 to be faced orexposed to the main chamber 18. The main valve 22 is endowed with arestoring force to close the main oil channel 28 by the action of aspring 31.

In this construction, the pressure in the high pressure side main oilchamber 12 or 14 acts from the main chamber 18 to the bottom end face32A of the valve shaft 32 directly. As the result, the response speed ofthe main valve 22 responsive to the change in set thrusting power of thelinear solenoid 26 can be increased as compared to the constructionshown in the prior art FIG. 1. However, with this construction, when asufficiently narrow orifice is provided to intensify the pressurereduction effect by the orifice 24 in order to improve the responsespeed at the step of raising the piston, the oil flow from the mainchamber 18 to the pilot chamber 20 is blocked, so that restoration ofthe main valve 22 is retarded to result in poor response property at therestoring step. On the contrary, when the orifice 24 be broader,sufficient pressure different (P_(m) -P_(p)) is not generated to resultin poor response property at the raising step.

The difficulties in accordance with the construction of the embodimentsshown in FIG. 2 can be avoided by providing a variable orificeinterconnecting the main chamber 18 and the pilot chamber 20 and a firstway in which this can be accomplished is shown in FIG. 3.

In this embodiment, a valve shaft 32 formed integrally with the plungerof a solenoid 26 is provided with a passage 34 which is elongated alongthe axial direction. The lower end of the passage 34 is opened on theouter periphery of the valve shaft 32 to form a variable orifice 36 incooperation with an opening provided on the side of the main valve 22.Thus, the variable orifice 36 has an opening area which is decreasedupon rising of the valve shaft 32 or upon lowering of the main valve 22.The top end of the passage 34 is opened to the pilot chamber 20.

The opening area of the variable orifice 36 is set to have apredetermined area in the condition as shown in the Figure where thevalve shaft 32 closes the pilot valve 30 and the main valve 22 closesthe main oil channel 28.

In this Figure, a pilot flow channel 38 (38a to 38d) is shown by thebroken line, and one-way valves 40 (40a to 40d) are interposedrespectively on the flow channels 38a to 38d.

Accordingly, when a force in the compressing direction (the directionshown by the arrow C) is applied to the piston 16 in the condition asshown in FIG. 1, the pressure in the high pressure side main oil chamber14 is applied through the pilot flow channel 38a, the one-way valve 40aand the main chamber 18 to the bottom end face 32A of the valve shaft32. Thus, as the pressure applied to the bottom end face 32A exceeds thethrusting force P_(s) of the linear solenoid 26, the valve shaft 32 israised. The pilot valve 30 is opened and the variable orifice 36 isclosed, accordingly. As the result, the pressure difference between thepilot chamber pressure P_(p) and the main chamber pressure P_(m) isincreased abruptly to raise the main valve 22 rapidly The valve shaft 32is moved to the position at which the thrusting force P_(s) of thesolenoid and the main chamber pressure P_(m) are balanced and the mainvalve 22 is moved followingly. As the main valve 22 is moved to broadenthe variable orifice 36, the pressure difference is decreased torestrict the movement of the main valve 22. Since the variable orifice36 has been thus broadened, transit of the oil from the main chamber 18to the pilot chamber 20 is carried out smoothly to effect restoration ofthe valve 22 rapidly under the action of the spring 31. Accordingly, theresponse properties of the main valve 22 at the rising and restoringsteps are improved. Similar operation sequence proceeds when a force inthe expanding direction (the direction shown by the arrow E) is appliedto the piston 16.

FIG. 4 is a view showing the principle of a second embodiment. Thisembodiment of shock absorber including a variable orifice has a fixedorifice 24A added to the passage 34 of the embodiment of FIG. 3. Indetail, the passage 34A provided in the valve shaft 32 is shortened andthe passage 34A becomes communicated with the pilot chamber 20 through afixed orifice 24A.

In the embodiment of preceding FIG. 3, the pressure difference isimmediately decreased as the variable orifice 36 is broadened so thatthe main valve 22 cannot be moved further. Accordingly, the position ofthe main valve 22 is limited by the stroke (stroke distance) of thevalve shaft 32 of the pilot system, so that the stroke of the valveshaft 32 cannot take so large range inherently, leading the result thatthe stroke of the main valve cannot be set to a large value.Accordingly, there is a problem that the adjustable range of the dampingpower cannot be set in a so large range. The embodiment of FIG. 4 is tosolve this problem.

In this embodiment, the pressure difference is rapidly increased bymeans of a variable orifice 36A to improve the response property of themain valve 22 at the rising step, and on the other hand, the pressuredifference between the pilot pressure P_(p) and the main chamberpressure P_(m) is lasted. In detail, as the main chamber pressure P_(m)ascends to raise the valve shaft 32, a variable orifice 36A is closedand the pilot valve 30 is opened to decrease the pilot pressure P_(p)rapidly. As the result, the main valve 22 is raised rapidly to open themain channel, so that the main valve 22 is raised at high speed. As theresult, the response property of the main valve 22 is improved.

Thereafter, as long as the pressure difference between the main chamberpressure P_(m) and the pilot chamber pressure P_(p) is kept at a valuehigher than a predetermined value by means of the pressure reducingfunction of the fixed orifice 24A, which has influence on the oilflowing therethrough, the main valve 22 is kept moving upwards. Thestroke of the main valve 22 is thus increased. As the result, the flowrate of oil flowing between both main oil chambers can be increased,whereby even a small damping power can be generated. Namely, by changingthe set thrusting power P_(s) of the solenoid, the adjustable rangethereof covers a larger range from a large damping power to a smalldamping power.

FIG. 5 is a view showing the principle of a third embodiment of shockabsorber including a variable orifice interconnecting the main chamberwith the pilot chamber. This embodiment comprises a main chamber facingto one end of the main valve 22A and having two partitioned portions 18Aand 18B, the pressure-bearing areas of respective portions 18A, 18B aredifferentiated from each other. In detail, an annular stepped portion isformed on the outer periphery of the lower portion of the main valve22A, the stepped portion being faced to one of the main chambers 18B,and the bottom end face of the main valve 22A is faced to the other mainchamber 18A.

By differentiating the pressure-bearing areas S₁, S₂ of the mainchambers 18A, 18B, the pressure for opening the pilot valve 30 relativeto the compressing and expanding directions of the piston 16 can becontrolled. With this construction, when it is intended to differentiatethe damping powers in the compressing and the expanding direction, itbecomes possible to vary the energizing current flowing through thelinear solenoid 26 within a narrower range to decrease the generatedheat thereby to lower the loading applied on the solenoid 26. Meanwhile,the pressures in the main chambers 18A, 18B are transmitted throughone-way valves 40a, 40c to a main pressure chamber 18C to act on thebottom end face 32B of the valve shaft 32 which faces to the mainpressure chamber 18C. In addition, by decreasing the diameter of the endface 32B of the valve shaft 32 facing to the main pressure chamber 18C,the driving thrust power required for the linear solenoid 26 can be setto a lower degree, whereby it is realized to speed-up the operation,compactmization of the solenoid 26 and saving of the driving electriccurrent.

FIG. 6 is a sectional view showing a practical construction examplebased on the third embodiment of shock absorber including a variableorifice. In this embodiment, the main chamber is partitioned into twoportions 18A, 18B, and one of the main chamber 18A serves also as themain oil chamber 14. In the Figure, the valve body 30A of the pilotvalve 30 is biased downwards by the plunger of the solenoid 26, and avalve plate 30B serving as the valve seat has a disk shape and is heldloosely over the whole peripheral side thereof in the radial directionto be movable. By the movement of the valve plate 30B, irrelevantengagement of the valve seat caused by inalignment between the valvebody 30A and the axis is dissolved.

The main valve 22B is formed to have a cylinder having a bottom andhaving an opening which opens to the pilot chamber 20A. A guide cylinder50 for the coil spring 31A is slidingly engaged with the interiorpheriphery of the main valve 22B and a damper chamber 51 is formed andsurrounds the outer periphery of the guide cylinder 50. An orifice 50afor communicating the pilot chamber 20A with the damper chamber 51 isprovided through the guide cylinder 50. A slight gap is left between theouter periphery of the guide cylinder 50 and the sliding surface of themain valve 22B. Vibration of the main valve 22B is suppressed by theresistance of flowing oil flowing, through the orifice 50a and theaforementioned gap, between the damper chamber 51 and the pilot chamber20A.

Meanwhile, the piston 16 is formed of a piston case 16A having an openlower end, a solenoid body 16B and a valve body 16C fitted in the pistoncase 16A in the described order from the bottom. The solenoid body 16Bcontains therein the linear solenoid 26, and has plural pilot flowchannels 38b which extend radially from the pilot valve 30. Each ofthese pilot flow channels 38b has an outer peripheral end at which aball-charge room 16Ba is formed to expand the outer pheripheraldirection, and a ball for forming a one-way valve 40b is charged intothe ball-charge room 16Ba. The open end edge 16Bb of the ball-chargeroom 16Ba is caulked to be inclined slightly bent towards the ball inorder to prevent fall-out of the ball to facilitate assembly of thepiston 16. The one-way valve 40b is opened when the upper main oilchamber 12 is in the low pressure side, and at that time the ball abutsagainst the interior surface of the piston case 16A.

The main valve 22B is mounted in the valve body 16C from the side facingto the solenoid body 16B, and an annular groove 16Ca surrounding themain valve 22B is formed on the face of the valve body 16C facing to thesolenoid 16B. This annular groove 16Ca is communicated with the lowermain oil chamber 14 through a proper number of pilot flow channels 38dextending through the axial direction. The annular groove 16Ca is alsocommunicated with the pilot flow channels 38b located in the solenoidbody 16B through a proper number of flow channels 16Bc. A one-way valve40d is formed by an annular plate valve mounted on this annular groove16Ca. The one-way valve 40d is opened when the lower main oil chamber 14is in the lower pressure side, and at that time the plate valve engageswith the stepped portion of the annular groove 16Ca formed on theinterior peripheral surface of the groove so that oil flows over theouter periphery of the plate valve.

A cylindrical body 52 is screw-fitted to the main valve 22B from theside of the lower oil chamber 14, and the cylindrical body 52 is fixedby a lock member 53 which is further screwed into the main valve 22Bfrom the downside. The fore end (top end) of the cylindrical body 52extends into the pilot chamber 20A. A main pressure chamber 18C isdefined in the cylindrical body 52. The pressure in the upper main oilchamber 12 is transmitted through a one-way valve 40c and the pressurein the lower main oil chamber 14 is transmitted through a bevelledone-way valve 40a to the main pressure chamber 18C.

The top end portion of the cylindrical body 52 is converged towards theinterior diametral direction to form a converged portion 52A to which anupwardly-extending pin 54, which projects from the interior of thecylindrical body 52, is engaged from the downside. This pin 54 has alower portion forming a cylinder 54C slidable within the cylindricalbody 52 and has a conical upper portion, from the top of which a pinportion 54B extends upwards. This conical portion opposes to the top endconverged portion 52A of the cylindrical body 52 from the downside.Meantime, a window 54A communicating through the interior of thecylinder 54C to the main pressure chamber 18C is provided at thevicinity of the outer periphery of the conical portion, so that oil canbe flown from the main pressure chamber 18C to the pilot chamber 20Athrough this window 54A. The fixed position of the cylindrical body 52is determined so that the pin portion 54B of the pin 54 abuts againstthe lower face of the valve body 30A of the pilot valve 30 under thecondition such that the conical portion forms a variable orifice havingan appropriate opening area is defined with the converged portion 52A ofthe cylindrical body 52.

With this construction, as the pressure in one of the high pressure sidemain oil chamber 12 or 14 is transmitted through the one-way valve 40cor 40a to the main pressure chamber 18C by the movement of the piston16, the pin 54 is pushed upwards. At the same time, the top end of thepin 54 pushes the valve body 30A upwards. Whereupon, the variableorifice in the pilot channel, which is formed by the pin 54 with theconverged portion 52A of the cylindrical body 52, is squeezed or closed.The pressure difference between the main chamber pressure P_(p) and thepilot chamber pressure P_(m) is thus abruptly increased to raise themain valve 22 at high speed. Although the variable orifice becomesenlarged by the rising of the main valve 22, the pressure difference iskept unchanged since there is a fixed orifice which is formed at the gapbetween the pin portion 54B and the converged portion 52A at the top ofthe cylindrical body 52. Accordingly, the stroke of the main valverelative to the moving distance of the pilot valve 30 is increased.

Still referring to FIG. 6, the main valve 22B extends from the openingof the main chamber 18B to the main oil chamber 14. Four pawls 22Baprovided on the main valve 22B to extending in the radial directionengage with the open edge of the main chamber 18B from the side of themain chamber 18B. At this time, only the pawls 22Ba engage with theopening edgflow e of the side of the main chamber 18B to close the mainchannel. Accordingly, even if the gap is under a reduced pressure by thesqeezing effect of the oil flowing through the gap, the force forattracting the main valve 22B to the side toward the main oil chamber 14is enfeebled. As the result, vibration of the main valve 22B issuppressed to smoothen the operation thereof. The interior bottom faceof the main chamber 18B is formed of a smooth conical face 18Ba. Theouter periphery 22Bb of the main valve 22B extending towards the mainoil chamber 14 is formed to be smoothly contiguous with the conical face18Ba to smoothen the oil flow.

FIG. 7 is a view showing the principle of a fourth embodiment of shockabsorber including a variable orifice interconnecting the main chamberwith the pilot chamber. This embodiment is an improvement of theembodiment of FIG. 3. In this embodiment, an annular stepped portion isformed, similar to the embodiment as shown in FIG. 5, on the end of themain valve 22A at the side of the main chambers 18A, 18B. This steppedportion is faced to one main chamber 18B, and the lower end face of themain valve 22A is faced to the other main chamber 18A. Since theportions or parts other than that described just above is the same asthose shown in FIG. 3, the description thereof will not be repeated.

According to this embodiment, similar to that of FIG. 5, thepressure-bearing areas S₁, S₂ of the lower end face of the main valve22A and the stepped portion are differentiated to set the pressures foropening the pilot valve 30 in the compressing direction and theexpanding direction can be independently set.

FIG. 8 is a view showing the principle of a fifth embodiment of shockabsorber including a variable orifice. In this embodiment, the biasingdirection of the linear solenoid 26 is reversed to that in theembodiment of FIG. 5. In detail, in the embodiment of FIG. 3, the linearsolenoid 26 biases the valve shaft 32 in the direction to close thepilot valve 30. On the contrary, a linear solenoid 26A of the embodimentof FIG. 8 biases the valve shaft 32 in the direction to close the pilotvalve 30 by means of a spring 26B, and the linear solenoid 26A attractsthe valve shaft 32 in the direction to open the pilot valve 30 uponenergization thereof.

As the result, in case where the linear solenoid 26A is deenergized bythe failure of the electric circuit, the spring 26B urges the pilotvalve 30 in the closing direction, and stable equiribrium is establishedat the position at which the force of this spring is balanced with theforce of the main chamber pressure P_(m) pushing the end face of thevalve shaft 32. Thus, the main valve 22 is held at the position at whichthe pushing force of the main chamber pressure P_(m) is balanced withthe pushing force of the pilot chamber pressure P_(p). Accordingly, whena failure occurs in the electric circuit during cruising of the vehicle,this shock absorber is held to exert a damping power which is balancedwith the spring force of the spring 26B to make it possible to allowcruising under such condition.

As has been described hereinabove, since a variable orifice (36) havingan opening area varied by the relative movement of a pilot valve (30)and a main valve (22) is provided in this invention, the operation speedof the main valve (22) can be increased to improve the responseproperty.

The variable orifice (36) may be provided by a passage (34) formed inthe valve shaft (32). By adding a fixed orifice (24A) to the passage(34), it becomes possible to lengthen the storke of the main valve (22)sufficiently.

The main chamber (18) may have a construction to transmit the pressurein the high pressure side main oil chamber (12 or 14) through theone-way valves (40a, 40c). By providing an annular stepped portion atone end of the main valve (22A) and by transmitting different pressuresin the main oil chambers (12, 14) respectively on the stepped portionand on the end face of the main valve to differentiate thepressure-bearing areas (S₁, S₂) of the stepped portion and the end faceof the main valve, the damping power may be variably set at theexpanding and the compressing directions. In such a case, the end faceof the main valve may be faced directly to one of the main oil chamber.

Furthermore, a cylindrical body (52) may be inserted through the mainvalve (22B) while forming a main pressure chamber 18C therein by theprovision of a pin (54) extending from the main pressure chamber 18C toabut against the valve body 30A of the pilot valve 30, whereby avariable orifice is formed by the pin (54) and the cylindrical body(52).

The shock absorber of the present invention, when used on a vehicle suchas an automobile, motor bicycles or like, can control independently thedamping power at the commpression side and the expansion side dependingon the crusing condition, and additionally the damping power can becontrolled intermediately of the storoke. Accordingly, the cruisingperformance of the vehicle can be improved to provide more comfortablefeeling to the driver or the rider.

I claim:
 1. A shock absorber comprising a cylinder, a piston in saidcylinder for defining two main oil chambers in said cylinder, a main oilchannel for communicating said two main oil chambers, a main valve foropening and closing said main oil channel, a main chamber facing to oneend of the main valve so as to transmit the hydraulic pressure in thehigh pressure side main oil chamber for biasing said main valve towardthe direction for opening said main oil channel, a pilot chamber facingto the other end of said main valve, a pilot valve for releasing thepressure in said pilot chamber to the low pressure side main oilchamber, a linear solenoid for biasing said pilot valve in a closingdirection, a variable orifice having an opening area varied solely bythe relative positions of said pilot and main valves, and a pilot flowchannel extending from said main chamber through the variable orificeand through said pilot valve to the low pressure side main oil chamber.2. The shock absorber as recited in claim 1, wherein the pilot valvecomprises a valve shaft having one end biased by said linear solenoidand another end extending through said main valve to face to said mainchamber, said valve shaft including a passage having one end openedthrough a variable orifice to said main chamber and the other end openedto said pilot chamber and defining at least in part the pilot flowchannel.
 3. The shock absorber as recited in claim 2, wherein saidpassage defined in said valve shaft is provided with a fixed orificeinterposed between said variable orifice and said pilot chamber.
 4. Theshock absorber as recited in claim 1, wherein an annular stepped portionis formed on the one end face of said main valve, said stepped portionand said one end face of the main valve being faced to a respective mainoil chamber for receiving the pressure of the respective main oilchamber, and wherein the pressures in these main oil chambers aretransmitted through respective one-way valves to the main chamber, thepressure-bearing area of said stepped portion being different than thepressure-bearing area of the one end face of the main valve.
 5. Theshock absorber as recited in claim 4, wherein the one end face of themain valve is directly faced to one main oil chamber to allow said onemain oil chamber to serve the main chamber, and wherein the pressure inthe other main oil chamber is transmitted to the main chamber which isfaced to the stepped portion.
 6. The shock absorber as recited in claim5, wherein a cylindrical body extending from the one main oil chamber toface to the pilot chamber is inserted through said main valve, a lockmember is thrusted into the cylindrical body from the one main oilchamber so as to define the main chamber, and a pin is provided toengage with a valve body of the pilot valve, said pin having aconical-shaped portion at its end to define a variable orifice with saidcylindrical body, a fixed orifice being formed by a pin portion of thepin and a converged portion of the cylindrical body at the open endthereof.
 7. The shock absorber as recited in claim 6, wherein thecylindrical body, the pin and the lock member are pre-assembled in themain valve.
 8. A shock absorber comprised of a pair of relativelymovable components defining a first fluid chamber, a second fluidchamber, a first conduit interconnecting said fluid chambers for flowtherebetween including a control valve for controlling the flow throughsaid first conduit, said control valve having a first surface exposed tothe pressure in said first fluid chamber and a second surface opposed tosaid first surface and exposed to the pressure in a pilot chamber, apilot valve for selectively communicating said pilot chamber with alower pressure area, a linear electrical solenoid for applying apredetermined closing force upon said pilot valve, and a second conduitcontaining a variable orifice interconnecting said first fluid chamberto said pilot chamber for transmitting therebetween, the effective areaof said variable orifice being determined solely by the position of atleast one of said valves relative to the other.
 9. The shock absorber ofclaim 8, wherein the effective area of the variable orifice iscontrolled by the relative positions of the valves.
 10. The shockabsorber of claim 8, wherein the shock absorber is a double-acting shockabsorber and wherein the first and second fluid chambers are defined onopposite sides of one of the relatively movable members.
 11. The shockabsorber of claim 10, wherein the effective area of the variable orificeis controlled by the relative positions of the valves.
 12. The shockabsorber of claim 10, wherein the control valve is supported within theone relatively movable member.
 13. The shock absorber of claim 12,wherein the control valve controls the flow in both directions betweenthe chambers.
 14. The shock absorber of claim 12, wherein the pilotvalve has a portion extending through the control valve and subjected tothe pressure in the first fluid chamber.
 15. The shock absorber of claim14, wherein the variable orifice is formed in part by the pilot valveextending portion.
 16. The shock absorber of claim 15, wherein thecontrol valve controls the flow in both directions between the chambers.17. The shock absorber of claim 16, wherein the control valve firstsurface is exposed to the pressure in a main fluid chamber and whereinthe main fluid chamber is connected to the first and second fluidchambers by respective passages containing check valves.
 18. The shockabsorber of claim 17, wherein the check valve passages are formed in thecontrol valve.
 19. The shock absorber of claim 18, wherein the controlvalve has a stepped end portion having an end face and a shoulderextending therearound and wherein the shoulder is exposed to thepressure in one of the fluid chambers and the end face is exposed to thepressure in the other of the fluid chambers.
 20. The shock absorber ofclaim 16, wherein a pair of check valved passages interconnect the pilotchamber, downstream of the pilot valve with the first and second fluidchambers wherein the pressure is dumped from the pilot chamber to thefluid chamber not being pressurized.
 21. The shock absorber of claim 20,wherein the check valve passages are formed in the one relativelymovable component.
 22. The shock absorber of claim 21, wherein thecontrol valve's first surface is exposed to the pressure in a main fluidchamber and wherein the main fluid chamber is connected to the first andsecond fluid chambers by respective passages containing check valves.23. The shock absorber of claim 22, wherein the passages containing thecheck valves are formed in the one relatively movable member.
 24. Theshock absorber of claim 22, wherein the passages containing the checkvalves are formed in the control valve.
 25. The shock absorber of claim24, wherein the control valve has a step end portion having an end faceand a shoulder extending therearound and wherein the shoulder is exposedto the pressure in one of the fluid chambers and the end face is exposedto the pressure in the other of the fluid chambers.
 26. The shockabsorber of claim 8, further including a fixed orifice in series flowrelationship with the variable orifice.
 27. A shock absorber comprisedof a pair of relatively movable components defining a first fluidchamber, a second fluid chamber, a first conduit interconnecting saidfluid chambers for flow therebetween and including a control valve forcontrolling the flow through said first conduit, said control valvehaving a first surface exposed to the pressure in said first fluidchamber and a second surface opposed to said first surface and exposedto the pressure in a pilot chamber, a pilot valve for selectivelycommunicating said pilot chamber with a lower pressure area, a linearelectrical solenoid for applying a predetermine closing force upon saidpilot valve, a second conduit separate from said control valveinterconnecting said first chamber to said pilot chamber fortransmitting pressure therebetween, and a portion of said pilot valveextending through said control valve for direct exposure to the pressurein said first fluid chamber for urging said pilot valve toward an openposition.
 28. The shock absorber as defined by claim 27, wherein thesecond conduit extends at least in part through the portion of the pilotvalve.
 29. The shock absorber as defined by claim 28, wherein theportion of the second conduit passing through the pilot valve portioncomprises a variable orifice the size of which depends upon therespective positions of the pilot valve and the control valve.
 30. Theshock absorber as defined by claim 29, further including a fixed orificein series flow relationship with the variable orifice and formed in thepilot valve portion.
 31. The shock absorber as defined by claim 27,wherein the second conduit extends through the control valve andincludes a fixed orifice.